[BEIJING] China's increasing air pollution has cut the light rainfall essential to the country's agriculture over the last 50 years, new research suggests.

The research, published in the Journal of Geophysical Research last month, is based on rainfall data collected from weather stations across China.

The number of light rain days — those with precipitation of less than ten millimetres — in northeast and southeast China has been cut by 25 per cent and 21 per cent respectively over the past five decades, researchers have found.

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"Analyses of air pollution data, satellite data, and large-scale circulation all suggest that aerosols may have played a more dominant role in the observed decrease trend in light rain in East China," the authors write.

Qian Yun, co-author of the research and an atmospheric scientist at the Pacific Northwest National Laboratory, United States, told SciDev.Net: "The decreased light rain will definitely deal a blow to agricultural potential in east China, the main food production area in China."

"Light rain soaks slowly into the ground [making it easier for the soil to absorb] which is better than heavy rain, which can flood fields and run off into nearby waterways."

The authors say that increased levels of aerosols — particles of pollution in the air above China — are caused by increasing fossil fuel consumption, particularly in big cities like Beijing.

They think that because rain drops form around aerosol particles, more particles means smaller drops that are less likely to form rain clouds.

Qian says the team will now build a model to calculate the agricultural and economic losses caused by air pollution to guide policymakers.

But Guo Jianping, a meteorologist at the Chinese Academy of Meteorological Sciences, who was not involved in the research, says the relationship between light rain and agricultural growth is difficult to define.

"Usually it is hard for small amounts of water to seep down into the ground and be absorbed. In addition, more rain days do not mean it's good for agriculture as less solar radiation is available," he told SciDev.Net.